Automatic plating current control system for electrolytic tinning apparatus



July 31, 1956 .1. G. PETROVICH ETAL 2,757,137

AUTOMATIC PLATING CURRENT CONTROL SYSTEM FOR ELECTROLYTIC TINNING APPARATUS Filed May 10, 1952 2 Sheets-Sheet 1 To PLAT/N6 BATH Fig. 1

INVENTORS JOSEPH 6. PE TROV/GH DONALD M. LEED) BY 44 MORNEY July 31, 1956 J. G. PETROVICH EIAL 2,757,137 AUTOMATIC PLATING CURRENT CONTROL SYSTEM FOR ELECTROLYTIC TINNING APPARATUS Filed May 10, 1952 2 Sheets-Sheet 2 W 0/vcc 2 INVENTORS JOSEPH 6. PETROL [CH DONALD M. LEEDY ORNEY United States Patent AUTOMATIC PLATENG CURRENT CONTROL SYS- TEM- FOR ELECTROLYTIC TINNING APPARA- TUS Joseph G. Petrovich, Gary, and Donald M. Leedy, Hammond, Ind.

Application May 10, 1952, SerialNo. 287,106 4 Claims. (Cl. 204-211) This invention relates to a control system particularly adapted for use in association and combination with continuous electrolytic tinning apparatus to maintain an optimum relation between the voltage of the plating current and the speed of the steel strip passing through the plating bath and receiving acoating of tin therein.

As is well known in the electrolytic tin coating, art continuous apparatus comprising an electrolytic bath of alkaline type for progressively plating on the surfaces of astn'pof indefinite length a coating of tin deposits approximately apredetermined weight of the latter metal per unit area of the strip surface only if the voltage of the plating current be maintained at a value ingeneral proportional to. the linear speed. of the strip through the bath.

Thus should the voltage of the plating current remain substantially constant when the speed of the strip decreases an excessive amount of tin is deposited thereon; this how ever does not necessarily impart to the more heavily coated portion of the strip greater commercial value as comparedwith an adjacent portion carrying a coating of the proper thickness but rather represents a waste of tin as well as electrical energy, while an increase in the speed of the strip, the voltage of the plating current. remaining constant, results in deposition of a coating of insufiicient thickness and may also cause defilming of the anodes in the electrolytic bath and thereby create a stannous tin condition which adversely affects the quality and hence commercial value of the resultant tin plate.

Largely because of difficulties incident toincreasing the plating voltage as strip speed increases it has heretofore. been deemed impractical particularly in an alkaline bathtinnin'g line to decrease the value of the plating current below its normal operating value when the speed of the. strip is temporarily decreased, occasional periods of slower than normal passage ofthe strip through the bath being substantially unavoidable in practice. Excessive thickness of tin coating has therefore customarily been deposited on the strip during such periods resulting, in wastage of the valuable coating material, supplies of which are now severely limited, and in excessive power consumption.

It is therefore a principal object of the invention to minimize the waste of tin in this manner in an alkaline tinningbath without incurring material risk of defilming the electrolytic plating anodes or the formation of stannous tin either during or following a subsequent increase in the speed of the stripthrough the plating bath.

Another object is to provide a system of automatic/control of the plating current supplied to an electrolytictinning apparatus or comparable unit by means of which the value of the said current is in general maintained in. substantially constant relation to the speed of the strip being plated, the value gradually increasing during gradual increases: and decreasing in corresponding manner during gradual decreases in the said speed, the said system including also meansforincreasing the value oftheplating current temporarily to. a predetermined maximum during a relatively rapid increase in the speed of the strip to thereby eliminate the effect of any lag in the normal operation of the automatic compensating elements which might otherwise result in the defilming of the plating anodes and/ or formation of stannous tin with consequent production of inferior tin plate through decline of the plating voltage to less than the critical minimum in relation to strip speed.

Other objects, purposes and advantages of the invention will hereafter more fully appear or will be understood from the following description of its embodiment in apparatus diagrammatically illustrated in the accompanying drawings wherein,

Fig. 1 is a conventionalized wiring diagram showing the several electrical and mechanical elements utilized in the system and the manner of their interconnection,- and Fig, 2 is a further conventionalized composite diagram of parts of the same system in which certain of the several involved circuits are extended more or less horizontally to facilitate tracing them in Fig. l.

The system diagrammed in the drawing as previously stated is designed to control the value of a plating current in an alkaline bath electrolytic tinning apparatus adapted and to obviate the production of areas of'strip of inferior quality, notwithstanding fluctuations in the strip speed which unavoidably occur in apparat'us ofthisgeneral nature, frequently for causes not related' directly to the plating operations.

As iswell known the weight of tin so deposited is proportional to the value of the plating, current when the values of all other pertinent factors remain constant and is in general inversely proportional to the speed of travel of the strip all factors other than strip speed are constant. ever during a rapid increase in the strip speed it has been substantially impossible to maintain a suitable increase in the value of the plating current without incurring the risk that due to a lag in the apparatus at some point or for other reasons the value of the plating current i the critical minimum value in relation to However, in accordance with our invention at the initiation of any such rapid speedin- Howtlie speed' increase has been effected and the speedof the strip. has become substantially constant at suchhigher rate.

Plating the invention 1s. concerned usually includes pinch rolls rate of linear travel of the strip; the latter rate is thus a' mathematical functionof the voltage supplied to the' pinch roll: driving motor and in accordance with this invention the said voltage isutilize I as a factor incontrolling the value of. the current supplied to'the plating bath.

Moreover the value of the platingcurrent is determinative of the amount of tin per unit area deposited ou the strip at a given speed' and this value is a mathematical function of the voltage in the circuit exciting. the field of the. generator producing, the plating current; the vo1t= agein' said circuit is" therefore subjected to controlby our novel system, and the plating generator voltage isa factor in initiating: certa'in automatic operationsleading to'modification of the value ofsaid voltage in? response tochanges in the: relation between thesaid value andth'e voltage in: the pinch rollmotor energizing: circuit. The said relation however is temporarily suspended-as. a controlling factor during a relatively rapid increase in the through the bath when voltage of the pinch roll motor circuit at the initiation of which the plating voltage is increased at once to an arbitrary maximum. It is then automatically maintained at that maximum for a predetermined period after the strip speed has increased to a constant higher value, and at the conclusion of that period control of the plating voltage in accordance with its relation to the pinch roll motor voltage is automatically resumed.

Thus in general the apparatus shown in the drawings includes a balancing relay having coils A and B energized respectively in proportion to the voltage in the armature circuit of a plating generator G1 and the armature energizing circuit of a pinch roll motor M1, the field P1 of which is energized through an adjustable field resistor PR. The said relay is operative when the coil A is energized sufiiciently to overcome the bias of the coil B to set into motion instrumentalities which reduce the voltage of the plating generator field exciting circuit and when the bias of the coil B sufficiently overcomes that of the coil A to operate the relay in the opposite direction to bring into play mechanism tending to increase the said voltage. To provide for a rapid increase in the voltage of the pinch roll motor armature energizing circuit a relay C in circuit with means (not shown) for effecting such increase is included in the system and when activated it sets in motion elements operative to immediately increase the plating generator field exciting voltage to a maximum and also to activate other instrumentalities including a timer T and a relay D associated therewith which automatically maintain said voltage at a maximum after the termination of the increase in voltage in the generator field F2 has ceased and the relay C is therefore deactivated as the pinch roll motor Ml resumes operation at a relatively constant although now increased speed.

it will of course be understood in connection with the circuits illustrated in the drawings that various leads designated as sources of electrical energy are connected to suitable power sources (not shown) providing circuits of a character appropriate for energizing the several elements connected with them in accordance with wellknown principles. Likewise it will be appreciated that whereas in many instances relay contacts of the single throw type are shown and certain such contacts are electrically connected together and actuated by the same relay, double throw contacts may be substituted for such pairs in these relays; in the description which follows references to these contacts as normally open contacts (NOC) and as normally closed contacts (NCC) are so abbreviated and such designations are accorded them in regard to the condition of the contacts when the mechanism actuating them is deactivated or deenergized, the contacts shifting either from open to closed or closed to open position in accordance with activation of their actu ating devices. A typical example of one of the latter is the relay E indicated in the drawing as containing one normally open and one normally closed contact designated hereinafter at NOC#ll and NSS#2 respectively of relay E although, to enhance the clarity of the drawings the several contacts of such relays are not identified therein by specific reference characters. They are however numbered in the description serially in the order in which they appear in Fig. 1 reading from left to right, the relay H being the only one illustrated having more than two contacts of any description under its direct control. It will be understood the plating voltage is controlled by the excitation of the field F2 of the plating current generator G1 and the circuits are therefore illustrated as applied to regulation of the field P3 of a generator G2 which supplies the plating generator field exciting current.

The coils A and B of the balancing differential relay referred to above are arranged to act in such manner that when the bias of one overcomes that of the other due to the voltage through one exceeding a predetermined value in relation to the voltage through the other a corresponding contact A1 or Bil as the case may be is closed and when the bias of the coils is in balance both said contacts are held open. The differential relay coil A is energized proportionately to the voltage of the plating generator armature circuit through its connection therewith by conductors 1, 2, 3 and 4, conductors l and '4 being connected respectively to poles of the generator armature; a battery X is interposed in the circuit of coil A between the conductors l and 2 with its polarity in opposition to that of generator G1 for a purpose which will hereafter appear, while the conductors 3 and 4 connect the coil A to the generator through normally closed contact NCCii'l of a relay 1 which under certain circumstances is energized to interrupt this circuit as later more fully explained.

Energizing conductors 5, 6 of coil B of the differential relay are in circuit across the armature leads of the pinch roll motor Ml energized from a generator G3, conductor 5 being connected directly to one pole of the motor armature supply and conductor 6 to the other pole through a resistor R1, conductor 7, a resistor R2 and conductor 8. Resistor R2 is desirably manually adjustable to allow proper compensation for various factors aiiecting the balance between coils A and B under given operating conditions, while a tap a on resistor R1 aifords a connection through which during certain periods in the cycle a portion of the resistor is kept shunted out of the circuit including coil B through NOC#2 of a relay K, the purpose of this arrangement being to minimize any tendency in coils A and B to hunt for a balanced condition when the plating generator voltage is at a proper value in relation to the strip speed for optimum condi tions and the tap a on the resistor is therefore manually adjustable to permit variation in the resistance shunted out.

Circuits controlled by the contacts Al and B1 of the diiferential relay are efiective to energize a motor M2, the direction of operation of which is determined by the polarity of its armature voltage; it is mechanically connected with the tap b of an adjustable resistor or motor driven rheostat MR1 which in series with a manually adjustable resistor R3 is interposed in the circuit exciting the field P3 of the gamer tor G2 under certain conditions of automatic operation and when relay H is deenergized so its NCC#3 and NCCit i in series with resistors MR1 and R3 are closed. Relay H when energized interrupts this circuit through the field P3 but its NOC#1 and NOC#2 close with. the opening of NCC#3 and NCC#4 and thus restore the circuit of said field but through a manually adjustable resistor R4 instead of through resistors MR1 and R3. NOCifill of a relay N is in series with the field F3 under either of the conditions just men tioned, the latter relay being kept energized through an automatic switch 0 while the plating line is in operation under automatic control.

From what has been said thus far it will be apparent on tracing the circuits in the diagram that when the voltage through the coil A is of such value with relation to that through the coil B as to cause the contact A1 to close as when the plating line is slowed down, relay K is energized therethrough and closes its NOC#2 thus shunting out a part of the resistance of resistor R1. Simultaneously NOC'tfil of relay K closes to energize in turn a relay 0 to close NOC-t i of the latter and open its NCC#2. NOC-iil of relay 0 in closing completes a circuit from main system energizing lead Ll through a conductor iii, NCC LSiiZ of a limit switch LS, a condoctor 11 and the armature of motor M2, the other lead 12 of which carries the circuit through NCCr-t?! of relay E and a conductor 13 to the main lead L2. This circuit being completed drives the motor M2 in a direction to adjust the rheostat MR1 in the appropriate direction to reduce the voltage in the field P3 of the generator G2; and this operation proceeds until the voltage through the coil A, which is proportional to the output voltage of generator G1, falls to a value relative to the voltage, in coil as increased during the closing of contact A1 by the shunting out of part of resistance R1 to balance the differential relay and thus allow contact A1 to open. The voltage through the coil B at this point is restored to normal for the assumed conditions, due to the entire resistance of resistor R1 being returned to its circuit by NOC#2 of relay K opening so that the voltage in coil A is not overbalanced by that in coil B, and contacts A1 and B1 therefore both remain open until the relation of their Voltages corresponding to a balanced condition is again departed from due to an increase or decrease in strip speed.

When the voltage in coil B increases in relation to that in coil A by a value sufficient to close contact B1, due for example to the pinch roll motor armature voltage being only moderately increased, relay E is energized and its NOC#1 thereupon through conductors 13, 1-1, 12 and 14, NCC#21 of relay and NCC LS#1 of limit switch LS completes the armature circuit of motor M2 at opposite polarity, conductor 11 now being connected to the lead L2 through NCC#2 of relay 0 and conductor 13, and conductor 12 to lead L1 through NOCa 'l of relay E, conductor 14, NCC LS#1 of limit switch LS and conductor It Resultant operation of the motor N1 in the opposite direction from that previously discussed thereupon actuates the motor driven rheostat MR1 to increase the excitation of the field P3 of the generator G2 and thereby increase the plating voltage until it has reached a value sufi'icient to restore the voltage in coil A to. a balance with relation to the increased voltage in the coil B and allow the contact 31 toopen. An incandescent lamp lL connected across conductors 11 and 12 indicates by lighting that a change is being made in the plating voltage.

Throughout the operations as thus far described the relay I has been assumed as deenergized and coil A of the balancing relay thus always in circuit across the terminals of generator G1, and it will be apparent that through interposition of the battery, X in this circuit in opposing polarity to the generator G1 a constant difference between the voltage of the plating generator and the voltage of coil A as well as a minimum limit of the plating voltage are maintained; the battery also-causes a lag in decrease of the plating voltage as the strip-speed is decreased and the voltage in coil B therefore reduced;

As has been mentioned it is desirable when the speed of the strip passing through the plating bath is rapidly increased that the plating voltage be increased to a maximum for a short period in order to avoid defilming of the plating electrodes and formation of stannous tin and-those portions of the system diagrammed in the drawing which produce such temporary increase in the plating voltage and hold it at a maximum until after the strip speed has reached a relatively constant higher value will now be described in greater detail.

The circuits utilized for this purpose include the relay C NOC.='#1 of which is held closed'during the plating voltage increase but allowed to open when contact d opens as the voltage reaches a relatively constant value and to remain open thereafter until a further relatively rapid increase in voltage or another such increase after an intervening decrease is effected. NOC#1 of relay C in closing energizes a relay P through conductors 15, 16 and 17, the relay P being so constructed that when it is energized its NCC#2 opens immediately but its NOCi-tl does not close until the elapse of an appreciable period of time thereafter and when it is deenergized its contacts again function successively but in opposite directions. Each time the relay P operates it leaves open for a brief period a short circuit through NOC#2 of relay N which when closed keeps a relay Q deencrgized. This causes relay Q to operate since although it is permanently energized through conductors 18, 19, a resistor R and conductor 20 the said short circuitin parallel with itzprevents its operation except during brief intervals on. energization 0r deenergi-z-ation of relay P when both NOCttI and NCC# 2 of this relayare open.

Consequently when relay P is energized during a relat-ivel-yrapid increase in the strip speed relay Q operates to close its NOC#1 and openits NCC#2, the former contact energizing relay I through conductors 25 and 26;, NCC#1- of relay D and conductors 27, 28 and 29 thereby opening NCC#1 of relay J and interrupting the circuit of coil A across the armatureof generator Git. Relay H is also energized by relay Q through NOCtil of the latter and a. conductor 30- while the opening of NCCitZ ofrelay Q prevents during this period energization of maintains its own energizing circuit through conductors 30-, 3'1, 27, NCC#1 of relay D and conductors 26, 32, 33 and 25 after deenergizati'on of relay Q. upon the closing of NOC#1 of relay P which again short circuits relay Q.

With. relay H thus kept energized through its NOC#5, its NO.C#6. is closed so that when theshort circuiting of relay Q thereafter closes its NCC#2 the relay D is energizedfrom 11-0 volt A.-C. leads L3 and L4 through conductors 3539, NCC#2 of relay Q and NOC#6 of relay H. The relay D-isconnected in parallel with timer T, also energized, from the leads L3 ductors 4.0, 41, 37,, 36 I NCC#2 ofrelay Q and NOC#*-6 of now energized relay H. The. timer T is adjusted to allow relay D to operate only after-it has been energizedfor a predetermined period. of, time, for example approximately six seconds, at; the conclusion, of which. the NCC#1. and NCC#2 of relay. D. are released to open and thereby dcenergize bothrelaysI-L andJ astwell asithetimer T but normally the strip speed increasezisr accomplished and relay C again opens, its; NOCtt l before the. timer can complete this cycle.

During the. period in-whichNOC #1 of relay C remains closed however, and with rleay H still energized, its NOCa'fil and NOC#2 remain closed to impress upon the field F.3ta maximum voltage'through conductors 42-49; NO,C#1 of: relay N, NOC#1 of, relay H, manually ad'- justable, resistor R4 and NOC#2. of relay H, conductors 42-, and 49 being connected respectively to the leads L1 The normal circuit: of field F3 through NCC#3* and' #4015 relay H and: resistors MR1, and R3 is during this period interrupted due to said NCCtl-Itand #4 being open;

Therelay I, initially energized by closing of NOC#1 ofrelayv Q, is kept energized through conductors 29, 28, 2-7, 26, 32, 33 and;25', NCC-#1 of relay D and. NOC#5 of relay H; NCC#1 of relay J being thus held'open keeps the, coil A- deenergized which allows the voltage in coil Bto, close the contact B11. The effect of this closing of course, as in the. operations, previously described, is to drive the motor M2 inadirectionto decrease the resistanceof motor driven rheostat. MR1.

Limit switch L8,, while not illustrated in the drawing as; mechanically connectedv with the motor M2 or re-- sistorMRl is desirably so located as to be operated there, by-to ope-11 the energizing circuit of the said motor M through NCC LS#1 or NCC LS#2of the switch as the casemay be, upon resistor MR1 reaching. a correspondinglimit of its mechanicaloperation.

The timer T is preferably adjusted so that when ini+ tially energized, and while thepinch roll motor voltage is increasing itdoes not complete its timing cycle but it resets itself to initiate a new timing cycle-when thepinchroll motor voltage again becomes constant.

Throughout the foregoing changes in the circuits.v of relays C, P, Q and D and timer T relay A remainsdeenergized and relays H. and J are energized. so maximumvoltage is impressed on field F3 through NOC#1' audit-2 of'relay'H. Butmotor M2 is being operated duringthis period, as aresult ofcontact B1 of the'dif ave /us? ferential relay being closed, to adjust resistor MR1 in the direction to reduce the resistance between conductors 50 and 51 until the limit of adjustment is reached and limit switch LS is actuated to open NCC LS# ll.

When NCC#2 of relay P closes, again short circuiting relay Q, and with relays H and I still energized NCC#2 of relay Q reenergizes relay D and timer T and on this occasion the timing cycle of the latter proceeds normally for the full period for which the timer is set, preferably about six seconds, during which the strip, now travelling at increased but substantially constant speed probably receives slightly more than the minimum desired amount of tin due to the voltage of generator Gll being maintained at its arbitrary maximum through NOC-F'i'l and #2 of relay H and resistor R4, the value of such maximum being determined by the adjustment of said resistor.

At the conclusion of said period the timer T operates to release relay D and permit it to actuate its NCCiil and #2 whereupon the timer energizing circuit through the latter is interrupted, allowing the timer again to reset itself in anticipation of an ensuing cycle while opening of NCCirl of relay D deenergizes relays H and I, the former thereupon restoring the circuit of field F3 to control through resistor MRll while NCCqil of relay J completes the balancing circuit of coil A and returns it to operative status for thereafter coordinating the plating voltage in relation to minor fluctuations in strip speed.

The motor M2 having been driven in the direction to increase the plating generator field voltage while the coil A was being held inoperative, this voltage initially causes an overbalance of coil B by coil A and the contact Bil therefore opens; in most instances the overbalance is sufficient to cause contact Al to close and thereby reduce the plating voltage, in the manner before described, to the proper value in relation to the now increased speed of the strip. The approximately correct plating generator field voltage is thereafter maintained automatically by the balancing of coils A and B in the normal manner until a further relatively rapid substantial increase in the strip speed either to a still higher value or following a subsequent decrease brings about a repetition of the operations for imposing a temporary maximum voltage.

The timer T may be of any suitable type, one adapted for the performance of its functions being available on the market as type TK manufactured by the Westinghouse Electric Corporation. It is adapted to automatically reset upon deenergization of the circuit which energizes it and the relay D so as to interpose a restraining period of predetermined duration upon operations of the said relay when the circuit is again energized in the manner heretofore described.

During normal operation of the system when relatively minor increases or any decrease in the strip speed occur and also when that speed is constant, the plating voltage is maintained at a proper value in relation thereto by the balancing coils A and B; moreover upon a major relatively rapid substantial increase in the strip speed the closing of switch [1 sets in operation that portion of the system which is efiective to increase the plating voltage to a maximum and to maintain it at that maximum for a brief period after the strip speed has become constant at the higher value. This temporary increase in the plating voltage as has been explained eliminates formation of stannous tin and prevents defilming of the plating anodes either or both of which tend to occur during a substantial increase in strip speed if the plating voltage is increased only proportionately.

As will be evident from examination of the circuits diagrammed in the drawings automatic operation of the system may be suspended without interrupting operation of the plating line by opening the switch and closing a manual switch a. The latter through conductors 70 and 71 energizes relays I and H the former of which, as during automatic operation, by its NCCtill holds open the energizing circuit of coil A while relay H by its NCC#3 and #4- disconnects resistors MR1 and 13 from the circuit of field P3 of generator G2 and interposes manually adiustable resistor in this circuit through NOCt l and #2 of relay H. Due to coil A being kept inoperative during manual operation motor M2 is operated through overbalance of that coil by coil B until limit switch L3 is actuated at maximum voltage position of tap b after which motor M2 remains deenergized until automatic operation is resumed. It will also he note that when the plating line is temporarily stopped and relay N therefore deenergized by opening of switch c the short circuit of relay Q is interrupted and the latter therefore energizes its NOCitll in turn energizing relays H and I with the results above described whereby maximum plating voltage is maintained at the resumption of operations and for a predetermined time period thereafter to insure the proper filming voltage after a line stop.

While we have herein described with considerable particularity one embodiment of the invention which is eminently satisfactory for the accomplishment for the purposes and objects thereof, utilizing as it does instrumentalities readily available on the market and adapted for mechanical and electrical interconnection in accordance with known principles, it will be understood that we do not desire or intend thereby to limit or confine ourselves to such embodiment in any way as changes and modifications in the construction and relationship of the several instrumentalities, their interconnection and operation will readily occur to those skilled in the art and may be utilized if desired without departing from the spirit and scope of the invention as defined in the appended claims.

Having thus described our invention, we claim and desire to protect by Letters Patent of the United States:

1. In apparatus for controlling the voltage of an electric circuit in accordance with the relation between the voltage in said circuit and the voltage in another circuit, a differential relay having opposed coils respectively connected with said circuits, voltage regulating means operative when actuated in one direction to increase the voltage of said first circuit and when operated in the opposite direction to decrease said voltage, means energized by said different relay for actuating said voltage regulating means respectively in opposite directions, means interconnected with the second circuit operative at the initiation of a rapid increase in voltage therein to interrupt the circuit through that coil of the relay connected with said first circuit and simultaneously to impose on said first circuit an arbitrary maximum voltage, and automatic means for maintaining said arbitrary maximum voltage on said circuit for a predetermined period after accomplishment of said increase.

2. In apparatus for controlling the voltage of an electric circuit in accordance with the relation between the voltage in said circuit and the voltage another circuit, a differential relay having opposed coils respectively connected with said circuits, voltage regulating means operative when actuated in one direction to increase the voltage of said first circuit and when operated in the opposite direction to decrease said voltage, means energized by said differential relay for actuating said voltage regulating means respectively in opposite directions, means interconnected with the second circuit including a relay responsive to relatively rapid increase in voltage in the second circuit relatively to the voltage in the first circuit operative to isolate said diiferential relay from effectiveness in relation to said voltage regulating means and simultaneously therewith to impose on said first circuit an arbitrary maximum voltage greater than normal relatively to the voltage of the second circuit and timing means operative to maintain said maximum voltage in said first circuit while the second circuit voltage is increasing and for a predetermined time thereafter.

.3. In apparatus for controlling the output voltage of a plating current generator having a field Winding, means for exciting said field Winding including a second generator also having a field winding, means operative substantially in correspondence with increases and decreases of the speed of linear travel through the plating bath of the article being plated to vary the exciting voltage to the field Winding of the second generator, means operative upon initiation of a rapid increase in said speed above a normal rate of increase to interrupt the operation of said voltage varying means and means operative substantially simultaneously with said interrupting means to impress a maximum exciting voltage upon the field Winding of the second generator and to maintain said voltage thereon until after termination of said abnormally rapid speed increase.

4. In apparatus for controlling the output voltage of a plating current generator having a field winding, means for exciting said field winding including a second generator also having a field Winding, means operative substantially in correspondence with increases and decreases of the speed of linear travel through the plating bath of the article being plated to vary the exciting voltage to the field Winding of the second generator, means operative upon initiation of a rapid increase in said speed above a normal rate of increase to interrupt the operation of said voltage varying means and means operative also upon initiation of such rapid speed increase to impress upon said field Winding of the second generator an arbitrary maximum exciting voltage and to maintain said maximum voltage thereon during said speed increase and for a predetermined time after establishment of constant speed at increased value.

References Cited in the file of this patent UNITED STATES PATENTS 1,400,092 Newbury Dec. 13, 1921 1,654,317 Ashbaugh Dec. 27, 1927 2,325,401 Hurlston July 27, 1943 2,488,856 Few Nov. 22, 1949 

1. IN APPARATUS FOR CONTROLLING THE VOLTAGE OF AN ELECTRIC CIRCUIT IN ACCORDANCE WITH THE RELATION BETWEEN THE VOLTAGE IN SAID CIRCUIT AND THE VOLTAGE IN ANOTHER CIRCUIT, A DIFFERENTIAL RELAY HAVING OPPOSED COILS, RESPECTIVELY CONNECTED WITH SAID CIRCUITS, VOLTAGE REGULATING MEANS OP ERATIVE WHEN ACTUATED IN ONE DIRECTION TO INCREASE THE VOLTAGE OF SAID FIRST CIRCUIT AND WHEN OPERATED IN THE OPPOSITE DIRECTION TO DECREASE SAID VOLTAGE, MEANS ENERGIZED BY SAID DIFFERENT RELAY FOR ACTUATING SAID VOLTAGE REGULATING MEANS RESPECTIVELY IN OPPOSITE DIRECTIONS, MEANS INTERCONNECTED WITH THE SECOND CIRCUIT OPERATIVE AT THE INITIATION OF A RAPID INCREASE IN VOLTAGE THEREIN TO INTERRUPT THE CIRCUIT THROUGH THAT COIL OF THE RELAY CONNECTED WITH SAID FIRST CIRCUIT AND SIMULTANEOUSLY TO IMPOSE ON SAID FIRST CIRCUIT AN ARBITRARY MAXIMUM VOLTAGE, AND AUTOMATIC MEANS FOR MAINTAINING SAID ARBITRARY MAXIMUM VOLTAGE ON SAID CIRCUIT FOR A PREDETERMINED PERIOD AFTER ACCOMPLISHEMENT OF SAID INCREASE. 